In the case of restraint, hot compressed gas, released from the gas generator, flows into the working space in order to displace the piston part. The traction transfer means, normally a traction cable, is at the same time exposed to high temperatures through direct contact with the hot compressed gas and can thereby be damaged. In buckle tensioners, in addition to the temperature load there is also a high traction load of the traction transfer means, which is exerted by the vehicle occupant moving forward. The traction transfer means is hitherto overdimensioned in order to be able to withstand the loads, which, however, has a negative influence on the manufacturing costs of the belt tensioner and also its weight.